Patent GB-142822-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/42
Filed: 1920-05-04
Abstract: 142,822. Western Electric Co., (Assignees of Polinkowsky, L.). May 5, 1919, [Convention date]. Automatic exchange systems; partyline systems.-In party-line systems in which provision is made for reverting calls, the subscribers' lines have access to two sets of line-finders, one set being used in the ordinary manner to extend a connexion to another line, the second set dealing only with reverting calls. Each party-line has two line relays 201, 202, Fig. 1, relay 201 being energized over the loop circuit and controlling in known manner ordinary line-finders, such as 277. The second line relay 202 is differentially wound, so that it is only energized when a subscriber, wishing to make a reverting call, depresses key 292 to earth the lower line. Relay 202 controls the second set of line-finders, each of which is associated with a ring-back equipment selectively operated by impulses sent by the calling subscriber. The ringing-equipment connects positive or negative current to one or other line, together with alternating current which energizes substation relays to connect up the polarized bells. Automatic release mechanism is arranged to restore the ringing- equipment if the subscriber does not proceed with the call in the usual manner. Connexion of calling line to second set of line-finders associated with ringing- equipment. A subscriber, desiring to make a reverting call, first depresses his key 292 and then removes his receiver. The depression of key 292 energizes the differential line relay 202, which connects a relay 203 in shunt to the other line relay 201 so that this is not energized by the removal of the receiver. Relay 203 starts the idle special line-finders, which hunt for the calling line in known manner under the control of the test relays 214, 212. When this is reached, the sequence switch 220 is moved into its fourth position, relay 222 being energized over its left-hand winding as it passes through its third position, and completing a circuit through its right-hand winding and the cut-off relay 207. If two line-finders come to rest on the terminals of the same line, one of them is released and its sequence switch 220 moved on by the common release mechanism shown on the right of Fig. 2 and referred to later. Operation of ring-back equipment. The stepping-relay 229, energized over the calling line, closer the circuit of a relay 231, which moves the switch 220 into its eighth position, in which the relay 223 is energized. The selective switch 100, structurally like a sequence switch, then moves automatically into its first position, connecting an interrupter 245 to the primary of a coil 224 in the line circuit, so that a dialling signal is given to the subscriber. The switch 100 is set by a single group of impulses in known manner under the control of a differential relay 239, auxiliary relay 237 and stepping-relay 229, At the last interruption of the line circuit, relay 229 de-energizes sufficiently long to energize a relay 234, which in turn energizes a relay 232, which moves the switch 220 into its eleventh position. The calling-subscriber then depresses his reverting ringing-key 296, which brings a condenser 294 into the loop circuit, thereby de-energizing relay 229, which causes relays 234, 232 to move switch 220 into its twelfth or ringing-position. It is assumed that the four ring- ing-positions of the switch 100 are positions 6, 7, 8, 9. Relay 226 or 227 is energized over contact 107 or 103 according as the switch 100 is stopped in positions 6 and 7 or 8 and 9. Alternating current superimposed on positive or negative direct current is thus connected over contact 109 or 110 to one or other line over the contacts of relay 226 or 227. The alternating current energizes relays 297, 298, 299 at the sub-stations, connecting up the polarized bells, so that only the desired one is rung. When the called party replies. the reduction in the sub-station resistance energizes relay 240, which closes a circuit for relay 230 which locks up and opens the circuits of relays 226, 277, 240. The partyline is now supplied with microphone current over relay 231 and coil 247, relay 231 moving the switch 220 into its eighteenth or talking-position. When both subscribers replace their receivers, relay 231 de-energizes and restores the apparatus to normal. Release if subscriber does not proceed with the call. A release mechanism, shown as a sequence switch 260 controlled by an interrupter 269, is arranged to restore the special line-finders &c. to normal if the call is not established within a reasonable time interval, or if the called party does not reply. The mechanism is common to a number of finders, and serves also to restore a finder when two finders simultaneously make connexion with the same calling line.